Many display devices exist within the market today. Among the displays that are available are thin-film, coated, electro-luminescent displays, such as OLED displays. These displays may be driven using active matrix backplanes, which employ an active circuit.
Stereoscopic displays are also known in the art. These displays may be formed using a number of techniques. Among the most commercially successful stereoscopic displays to date have been displays either employing some method of shuttering light, such that the light from one frame of data is able to enter only the left or right eye at any point in time and left and right eye images are shown in rapid succession. Two primary methods have been employed in this domain; including displays that employ active shutter glasses or passive polarizing glasses. For example, Byatt in U.S. Pat. No. 4,281,341, entitled, “Stereoscopic Television System” described a system employing a switchable polarizer that is placed in front of a CRT and is viewed with glasses; wherein each lens of the glasses transmits light having one of the two polarization states that are passed by the switchable polarizer. In such a system the polarization is switched to select which eye will see the display at any instant in time; and by synchronizing the display of images with the switching of the polarizer, the system can display a different image to each eye of the observer. Temporal updates of stereoscopic information using techniques such as these enables a user to see the full resolution of the display and enables switching from a monoscopic to a stereoscopic viewing mode. Unfortunately, the disadvantage of such a system is that the update rate of the display and the switching element must be quite high to avoid the perception of flicker. Therefore, required refresh rates of at least 60 Hz per image are provided to each eye; and even higher refresh rates are desired.
Unfortunately, refresh rates significantly higher than 60 Hz can be difficult to attain in large active matrix thin-film electro-luminescent displays, such as OLED displays. In these displays, the active circuitry is separated from a sheet electrode, often the cathode, by only 100 to 200 nm of material having a dielectric constant often in the neighborhood of 3. As such, a significant capacitance can exist between the active matrix drive electronics, particularly data lines within the active matrix circuitry and other elements within the display, particularly the sheet electrode within the display. This capacitance can create a significant RC constant and limit the update rate at which data may be clocked into pixel circuits to rates below 120 Hz, particularly in larger displays where the resistance of the data lines can be significant.
Another issue with using conventional shutter glasses or full screen switching polarizers is discussed by Chang in U.S. patent application Ser. Nos. 11/200,270 and 11/200,774, each entitled “Method and apparatus for stereoscopic display employing an array of pixels each employing an organic light emitting diode”. As discussed, these displays are often updated one line at a time and provide light for the entire time between updates. As such, Chang describes a stereoscopic organic light-emitting diode display in which a first eye's image is blanked before the second eye's image is displayed. In a stereoscopic display in which the entire image is updated by a stereoscopic overlay, this blanking interval reduces the crosstalk between the left and right image. In a particular implementation, depicted in FIG. 5a of their disclosure and reproduced in FIG. 1 of this disclosure, a circuit is provided that allows a left eye image to be written into a portion of the circuit 2 and then displayed while the right eye image is written into a separate portion of the same circuit 4. That is, the TFT 10 can control power to the OLED 8 such that if each of these transistors in each circuit in the entire display are controlled simultaneously, every OLED in the entire display may be activated or deactivated simultaneously. As such, an entire image for one eye may be written into each circuit in the display while a second portion of the same circuit is used to display the image to the other eye, allowing the on time for each pixel in the display to be synchronized with the optical switch. As such, cross talk is reduced. Notice, however, that this circuit controls the current from the power supply Vdd 6 through two of the TFTs (e.g., 12a, 12b) in each portion 2, 4 of the circuit to the OLED 8. Since these TFTs 12a, 12b must provide current to illuminate the OLED; they will typically be required to be large TFTs to support this current load. Further, this prior art circuit has a large number of additional transistors and connecting wires, which complicate the circuit; uses large amounts of backplane real estate (limiting display resolution); and will require very high yield rates to allow successful manufacturing of a working active circuit. Therefore, this particular prior art circuit is relatively large and can be expensive to implement. Further, the circuit does not provide a method for reducing flicker as the image update, delayed by the display, is restricted to the same update rate.
Circular polarization has also been used in systems to provide images without flicker or with the cross-talk that occurs as the update of the information and the optical switch are not synchronized for each pixel in the display by using an approach that is similar to that employed in barrier screen displays. Lipton in U.S. Pat. No. 5,686,975, entitled, “Polarel Panel for Stereoscopic Displays” and Ma in U.S. Pat. No. 6,020,941, entitled, “Stereographic liquid crystal display employing switchable liquid crystal materials of two polarities in separate channels” each describe display systems where alternating columns of a display device are each provided with circular polarizers that are arranged in columns, such that alternating columns provide light that is circularly polarized with left and right handed orientation. By changing the handedness of the polarization in this way, and by wearing polarized glasses, each eye is provided alternating columns of the information from the display. However, as the handedness of the polarization of the light is kept constant during display of stereoscopic imagery, the resolution is reduced due to the fact that each eye can only see half of the columns of the display while viewing stereoscopic imagery. Faris in U.S. Pat. No. 5,844,717, entitled, “Method and system for producing micropolarization panels for use in micropolarizing spatially multiplexed images of 3-D objects during stereoscopic display processes” and Faris in U.S. Pat. No. 6,359,664, entitled, “Electro-optical display system for visually displaying polarized spatially multiplexed images of 3-D objects for use in stereoscopically viewing the same with high image quality and resolution” have described similar displays that provide stereoscopic images by arranging a two-dimensional array of micropolarizers on a display surface with each eye being able to see a checkerboard pattern of the image. However, because each of these embodiments employ static methods of controlling the light seen by each of the user' eyes the perceived resolution of the display is reduced by a factor of at least two.
Lenses may be formed over the display to provide stereoscopic information as described by Tutt et al. in US patent application Number US200739859, entitled, “3D or multiview light emitting display” or dynamic lenses as described by Woodgate and Harrold in the Society for Information Display Journal article entitled, “Efficiency analysis for multi-view spatially multiplexed autostereoscopic 2-D/3-D displays” may be used to provide multiple views of a display to multiple locations in space. However, when the display is not updated temporally, the effective resolution of the display is reduced; and when it is updated temporally, high update rates are required.
Hattori et al. in U.S. Pat. No. 7,068,252, entitled, “Display unit capable of displaying two- and three-dimensional images and method for controlling display unit” and in U.S. Pat. No. 7,066,599, entitled, “Display unit” discuss the formation of a barrier screen for limiting the path of light to one of two angles corresponding to different points of view. This screen is switchable, such that the direction of the light is changed between refreshes of the stereoscopic overlay, allowing the light from one pixel or region of a display to be transmitted to one eye within one time interval; and the light from the same pixel or region of the display to be transmitted to the other eye within a subsequent time interval. One could apply such a barrier screen with an OLED display. Unfortunately, the EL display would require a high refresh rate; and because the barrier screen is switched for an entire column, such a barrier would generally not be synchronized with pixel updates within an active matrix EL display.
Sun and Lao in U.S. patent application Ser. No. 11/092,889, entitled, “Dual polarizing light filter for 2-D and 3-D display” discuss a display overlay capable of switching between two polarization states on a pixel-by-pixel basis. By using such an overlay, two different polarization states may be imparted to the light passing through any pixel in the overlay, within any time interval. Miller et al in U.S. Pat. No. 7,221,332, entitled, “3D stereo OLED display” describe the use of a similar display structure with an OLED display in which the switching of the polarization states is synchronized with the update of information on the OLED display. While this latter patent recognizes that the update rate may be limited, it does not provide methods for increasing the effective refresh rate of the display.
Each of the prior art discussions of EL display implementation have involved methods for modulating the output of the EL light-emitting diodes within the display by modulating an analog signal, which modulates the current through the EL device. However, in addition to these analog drive methods, it is also known to drive EL displays with digital drive methods as discussed by Kawabe in International Publication Number WO 2006/020511, entitled, “Emissive display device driven in subfield mode and having precharge circuit”. As described in this publication, each EL light-emitting diode may be provided with either no current or a single fixed current and the light output by the light-emitting diode may be modulated by changing the duration of this light output. In such embodiments, each frame time is divided into a number of subfields, requiring that the signal to each light-emitting diode be switched multiple times during each frame. However, the refresh rate (i.e., the number of frames provided each second) is limited by the capacitance and resistance of the display structure as it is limited for the analog drive methods and has the additional constraint that data for multiple subfields must be provided within each frame.
A method is needed, therefore, for increasing the effective update rate of an EL display to allow flicker-free presentation of stereoscopic, 3D or other information. Such a method should also be effective in reducing cross-talk between left and right eye images in EL displays.